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Objectives and IntroStandard Model of Carcinogenesis








Acute phototoxic reaction
Acute phototoxic reaction




Ultraviolet light is the most important carcinogen for the genesis of skin cancers.

  • ultraviolet C
    • highly carcinogenic, with wavelengths < 290 nm
    • however, it does not reach the earth surface in significant amounts because of ozone layer
  • ultraviolet B
    • most carcinogenic band that reaches earth in significant quantity
    • band of ultraviolet radiation between 290 and 320 nm
    • ubiquitous during daylight hours
    • directly damages DNA, causing strand breaks and nucleotide dimer formation
    • vitamin D is produced mainly by UVB, but some can be produced by UVA
  • ultraviolet A
    • is light between 320 nm and 400 nm
    • a weak carcinogen by itself, but in combination with UVB has significant additive effect
    • major carcinogenic effects of large amounts of UVA are in the band between 320 and 340 nm
    • biologic damage is direct, similar to the type induced
      by UVB
    • between 340 and 400 nm, damage is indirect through other activated photosensitizers within the cell, which
      in turn interact with DNA
    • ultraviolet A in longer wavelengths is an important cause of wrinkling of the skin

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